1. Field of Invention
The present invention relates to a video communications system and more particularly to a video communications system capable of compressing information that represents an image, particularly, a dynamic image i.e. a moving picture, of multiplexing and storing the information and audio data and finally of regenerating and decoding the stored information.
2. Description of the Background Art
Recently, in addition to conventional communications services, i.e. telephone and facsimile, audio storage and delivery services have been available over certain networks to allow audio data to be stored temporarily until a particular destination terminal was available.
The progress in digital communications networks, i.e. ISDN (Integrated Services Digital Networks) enables the terminal users to receive video communications services by means of visual telephone terminals. With such a background, there is an increasing demand for video storage and delivery services which are put into practice with certain local applications.
In a conventional video communications system, an input video signal through the camera of the transmitting terminal enters into the encoding portion whereby it is encoded with stored amounts of information by an interframe predictive coding method. On the other hand, an audio signal input through the handset is encoded by the audio encoding portion. Both encoded video and audio signals enter into the multiplexing portion whereby they are combined with each other and completed with a video control signal designated by the terminal system control unit after which they are sent to the communications network. The multiplexed data is transmitted over the network to the remote terminal wherein the data is separated into individual signals i.e., a video signal, an audio signal and a video control signal by the action of a multiplexing portion. The video control signal, the video coded signal and the audio coded signal are transferred to the system control unit, the video decoding portion and the audio decoding portion, respectively. In the video decoding portion, the video data encoded by the interframe predictive coding method is decoded and then is put out to create an image on the screen of the monitor. In the audio decoding portion, coded audio data is decoded and put out to the handset. The video control signal is treated by the system control unit. The above-mentioned actions are conducted through a two-way transmission line to produce bidirectional visual telephone communications.
The interframe predictive coding method is such that video data of a predicted picture is encoded in a compressed form to include only differential data between a standard updated picture and the succeeding picture, utilizing a very strong correlation between the frames of the moving picture data. This method enables us to considerably reduce the number of video data needed to be transmitted since the predicted picture includes a very small amount of data in comparison with the updated picture. The header information is attributive information attached, when coding, to the beginning of the corresponding frame of video data. The updated picture is one frame of video data encoded therein in the same way as a still picture, and after coding, it has a number of coded data equivalent to that of the still picture. The interframe predicted picture is defined by determining the difference between the updated video data and the video data of a subsequent frame and it is represented as a frame which includes only differential data.
In a conventional video storing and reproducing system utilizing still pictures, the host and the terminal are connected to a communications network (such as ISDN) and operate to gain access to each other at the host's or the terminal user's request. When a circuit therebetween is established, a guiding picture from the host is displayed on the screen of the monitor. Referring to the guiding display, the terminal user selects a menu for storing or reproducing video signals by one frame representing a still image with a audio signal. The video signal to be stored in the memory is input through the camera and an audio signal to be stored is input through the handset. The input video and audio signals are encoded respectively by the video encoding portion and the audio encoding portion and then they are transmitted over the communications network to the host which in turn combines and stores the received encoded video and audio signals in the storage device.
A set of data is described in such a way that a packet of one-frame video data is combined with the audio data having an identifying flag and the character data also having an identifying flag. The number of bits in a packet of video data depends upon the types of video signals to be encoded but it may not largely vary since coding is achieved within one frame. Therefore, the audio data has no considerable variation in its length. Sometimes an image may contain character data, and sometimes it may contain none. However, the amount of character data per scene is much smaller than that of the video data and, therefore, it is negligible.
The prior art for which the present invention was made is disclosed in the technical report titled "CODEC for video delivery services and video Conference services" of IEIEC (Institute of Electronics, Information and Communication Engineers) No. IE93-41, 1993-07. The prior art dealt with the same contents and the same users system of communication services as the present invention but it proposed that each terminal periodically perform in-frame coding to make the data suitable for storage and reproduction.
On the contrary, the present invention provides that universal visual telephone terminals be used and that the communications center makes the data adaptable for storage and reproduction.
On the other hand, the present invention relates to a data multiplexing system which enables all stored data, including video signals, to be reproduced in conformity with the communications conditions that will assure broad utilization of storage and forward communications services by means of terminals such as universal visual telephone equipment.
As mentioned above, the conventional video delivery services must have center facilities to generate information, change the stored data, convert the media and the stored data by half. On the other hand, the data multiplexing method currently used in video communications, i.e. visual telephone communications, combines the data of each half by a bit. If the multiplexed data is stored as is, the center processor can hardly generate any information or change it.
In the case of realizing video delivery services including dynamic images, the video transmitting format currently applied, for example in visual telephone services, utilizes the interframe prediction technique for compressibly encoding the video data and therefore it may have a certain amount of information per frame which considerably differs from the format utilizing the interframe predictive coding. Consequently, when packets for storing video and audio data according to video signals per frame are formed, the packets may differ from one another in the size and the amount of information to be stored. This may cause the discontinuation of the data's flow when reproducing the stored video data in a certain sequence. Since the conditions of the communications between the terminals may be changed at any time, it is impossible to use a packet of a fixed structure.
The conventional coding method may be applied by increasing the number of frames of still images without using an interframe predictive coding to simulate dynamic images. In this case, the quantity of data encoded without interframe prediction is ten times larger than that of the data encoded by the interframe predictive coding. An attempt to transmit data necessary for regenerating an image to be observed as it moves, leads to an increase in the cost of the transmission. This may also require an increase in the capacity of a transmission line.